It is known that nitriles are formed by addition of HCN to an unsaturated carbon-carbon bond, e.g. the double bond of an olefin. However, in view of the risks involved in handling this highly toxic chemical, this addition method is considered unsuitable for large scale operation. Hence various attempts have been made to develop a method for producing nitriles whereby the use of HCN is avoided.
From U.S. Pat. No. 4,456,562 a process for producing nitriles is known whereby a compound of the formula R--CHO is reacted with a hydroxylamine-inorganic salt. In the event that R represents an aromatic group, the nitrile is directly produced whereas compounds in which R represents an alkyl or alkenyl group are converted in a first reaction step to an aldoxime from which in a second reaction step by dehydration, the nitrile is formed.
In NL 105,424 a one step method is described whereby
at moderate reaction conditions (reaction temperatures of 20.degree.-40.degree. C. and atmospheric pressure) nitriles are produced from primary alcohols or aldehydes and ammonia in a liquid alkaline medium under the influence of copper compounds.
The aldehydes (or alcohols) which are used as starting material in these known processes have to be prepared in a separate step, preceding the conversion into nitriles. For the preparation of the aldehydes, conventional methods can be applied. Accordingly aliphatic aldehydes with three or more carbon atoms can be obtained from olefins, carbon monoxide and hydrogen under the conditions of the Oxo process, i.e. at moderate reaction temperatures and at relatively high pressures, e.g. of 150 bar and higher (cf "New Syntheses with Carbon Monoxide" by J. Falbe, p. 30,97). It would be advantageous, if nitriles could be prepared directly from olefins at moderate reaction conditions and, of course, without involvement of HCN during the process.
It has now been found that by selecting particular reactants and catalysts, nitriles are directly obtained from the unsaturated compounds used as starting material.